1. Technical Field
This invention relates to the art of designing and fabricating pistons and related heat engine component surfaces for a fossil fueled engine, which surfaces affect the conversion of chemical energy to mechanical energy and which affect emissions resulting from the combustion process; more particular the invention relates to combustion chamber and charge induction surfaces, including piston designs and materials that (i) can store and release heat selectively, (ii) control or limit temperature of piston and component surfaces, or (iii) control or inhibit thermal expansion of components, primarily pistons, in an internal combustion engine (IC).
2. Discussion of the Prior Art
In heat engines, such as IC engines (gasoline or diesel) used in automotive vehicles today, some of the heat of combustion gases is siphoned off through a thermal path that proceeds through the piston (which is usually constructed of aluminum alloy in a gasoline engine), through the piston rings, to a metallic engine block and cylinder head that are cooled by a water jacket that in turn dumps such heat. Such parasitic heat loss limits the available power and engine efficiency. Because of the dynamics of the combustion cycle and the heat transfer characteristics of an IC engine, a significant amount of heat along such thermal path is stored in these components during the combustion and exhaust portions of the engine operating cycle. A part of this stored heat is transferred to the fuel/air charge during the intake and the compression strokes (e.g. 4-cycle engine). This is particularly disadvantageous for the operation of a spark ignition gasoline engine; its compression ratio will be determined by the knock-limit and therefore the compression ratio is chosen to avoid engine knock resulting from auto ignition. However, the higher the knock-limited compression ratio, the higher will be the power and engine efficiency. Conversely, for every one point reduction in the compression ratio, due to such design limitations, there is a corresponding reduction in engine fuel economy of about 2-2.5 percent and a 2.5-3.0 percent loss in engine power. The compression ratio is reduced because high compression would more readily heat up a less dense gas to above the knock temperature limit.
It would be desirable to preserve as much of the heat of combustion to do mechanical work during the combustion/expansion stroke for driving the vehicle. In the case of the spark ignition engine, it is desirable to control the heat input into the charge from the piston, or other combustion chamber components, during the intake stroke, thereby increasing volumetric efficiency of the engine. Stored heat that is transferred to the induction charge should only be enough to improve either evaporation of the fuel for avoiding condensation on the bore wall. In the case of a diesel engine, after engine warm-up, the charge air density is more important. Unlike the spark ignition engine, the warmer the charge after the intake valve closes, the better it is for engine operation because of reduced ignition delay which improves engine combustion. it would also be desirable to control the thermal expansion characteristic of the piston body adjacent the piston crown when managing such thermal conditions.
Attempts by the prior art to thermally manage heat flow through pistons have been restricted to the use of certain types of thermal barriers (Teflon in U.S. Pat. No. 2,817,562; nickel metal in U.S. Pat. No. 5,158,052; and chromium oxide in U.S. Pat. No. 4,735,128). Such thermal barriers are insufficient to manage heat properly because they must be unduly thick thereby adversely affecting volumetric efficiency (i.e. allowing too much stored heat to be transferred to the induction charge); no provision is made to remove the stored heat from the combustion chamber surfaces independent of charge absorption.